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Ann Thorac Surg 2000;70:1546-1550
© 2000 The Society of Thoracic Surgeons
a St. Vincent Medical Center, Los Angeles, CA, USA
b Providence St. Joseph Medical Center, Burbank, CA, USA
c St. Johns Regional Medical Center, Oxnard, California, USA
Address reprint requests to Dr Baumgartner, 2200 W 3rd St, Suite 300, Los Angeles, CA 90057
| Abstract |
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Methods. Our database of 242 OPCAB patients undergoing complete revascularization was compared to a base of 483 CABG patients undergoing CPB. Results were compared for the overall series and in the following high-risk subsets: 80 years of age or older, ventricular dysfunction (ejection fraction (EF)
0.25), prior neurologic event or renal failure, chronic obstructive pulmonary disease (COPD), and reoperation.
Results. In the overall series, OPCAB significantly reduced the incidence of intraoperative transfusion requirements and showed a trend toward reduced morbidity in terms of postoperative neurologic and renal complications, prolonged ventilator requirement greater than 3 days, and bleeding requiring reexploration. Mortality was less in the OPCAB group (0.4% versus 2.7%, p = not significant). Similar results were achieved in the following high-risk subgroups (n = off-pump/on-pump): 80 years of age or older (n = 28/58), EF less than or equal to 25% (n = 13/26), preoperative neurologic event (n = 25/36), preoperative renal failure (n = 27/46), COPD (n = 33/43), and reoperation (n = 28/76). OPCAB decreased the incidence of prolonged ventilation in COPD patients (0/33 [0%] versus 4/43 [9.3%] p = not significant) and decreased the incidence of renal complications in the elderly (1/28 [3.6%] versus 9/58 [15.5%] p = not significant). Off-pump coronary bypass reduced but did not eliminate neurologic events in the elderly (2/28 [7.1%] versus 8/58 [13.8%] p = not significant).
Conclusion: Off-pump coronary bypass significantly reduced the incidence of transfusion requirement compared to the CPB counterparts and had a consistent trend in reducing morbidity and mortality overall and in all high-risk subsets. Neurologic events are not eliminated in OPCAB.
| Introduction |
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Minimally invasive direct coronary bypass and off-pump coronary bypass (OPCAB) have eliminated one major component of aberrant physiology intrinsic to on-pump coronary bypass procedures. Coronary bypass, without the use of cardiopulmonary bypass (CPB) has been shown to reduce the overall systemic inflammatory response, including cytokine-mediated responses [46]. Furthermore, cardioplegic arrest adds an additional level of physiologic derangement directly upon the heart, and troponin I release and myocardial injury are reduced in off-pump procedures [4, 7]. The implications for specific organ systems are that elimination of CPB would lead to a more physiologic mileau that would encourage optimal organ function during and immediately following coronary revascularization. This conceivably might reduce organ-specific complications, especially in high-risk subgroups.
The present study attempts to evaluate whether the theoretical advantages from eliminating CPB from coronary revascularization are translated into a decreased morbidity and complication rate in these patients. The series as a whole, as well as specific high-risk subgroups, are compared between off-pump and on-pump groups.
| Patients and methods |
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0.25 as assessed by left ventriculography or transesophageal echocardiography or both); 80 years of age or older; preoperative neurologic event (stroke or transient ischemic attack), preoperative renal failure (creatinine > 2.0 mg/dl and/or dialysis dependence), chronic obstructive pulmonary disease (COPD) as documented by altered pulmonary function tests or clinical or radiographic emphysematous changes; or reoperative coronary surgery. OPCAB was done by full median sternotomy [8] or by left posterolateral thoracotomy in instances of reoperative coronary revascularization to obtuse marginal vessels in patients with patent left internal mammary artery grafts [9]. The OPCAB generally was not done in patients with extremely small, heavily calcified, or intramyocardial targets, or those with massive cardiomegaly. Severe ventricular dysfunction was not a contraindication to OPCAB. Standard CABG was done with full cardiopulmonary bypass, tepid cooling, and antegrade and retrograde cold blood potassium cardioplegia.
As a general rule, indications for intraoperative blood transfusion in patients undergoing CPB include a preCPB hematocrit less than 32%, hematocrit less than 19% on CPB, or hematocrit less than 26% immediately postCPB. In OPCAB, a hematocrit less than 28% during the procedure was an indication for transfusion.
Operative and postoperative variables between the groups that were investigated included use of intraoperative blood transfusions, 30 day operative mortality, neurologic complication (stroke, transient ischemic attack, or prolonged mental status changes), renal complication (creatinine elevation above 2.0 mg/dL or need for hemodialysis, when these were not preoperatively present), prolonged ventilator dependence beyond 3 days, postoperative bleeding requiring reexploration, and postoperative critical care unit (CCU) and hospital stays. Statistical comparisons were done with the Chi-square and Yates correction.
| Results |
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Preoperative risk factors were similar between the two groups. The preoperative incidence of COPD, preoperative stroke or transient ischemic attack, and renal insufficiency for the OPCAB versus on-pump groups was 14% versus 9%, 12% versus 8.3%, and 11% versus 9.5%, respectively. The incidence of ejection fraction less than or equal to 0.25, age 80 years or older, or reoperations for the OPCAB versus on-pump groups was 5% versus 5%, 12% versus 12%, and 12% versus 16%, respectively. Diabetes mellitus and peripheral vascular disease were present in 34% versus 29% and 12% versus 15% of the OPCAB versus on-pump groups, respectively. The mean age was 67 years for the OPCAB and 68 years for the on-pump groups.
The overall series 242 OPCAB and 483 on-pump cases is compared in Table 1. The mean number of grafts were 3.1 and 4.0 for the off-pump and on-pump groups, respectively. OPCAB significantly reduced the number of patients requiring intraoperative blood transfusion. Although the OPCAB series exhibited a trend of reduced operative mortality, neurologic and renal complications, prolonged ventilator dependence beyond 3 days, and postoperative bleeding requiring reexploration, none of these variables reached statistical significance. Postoperative critical care unit and hospital days were similar between the groups, although slightly less in the OPCAB group.
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For the subgroup with ejection fraction less than or equal to 0.25, apparent advantages of OPCAB compared to on-pump cases were less pronounced, with the exception of a marked decrease in the incidence of introperative blood transfusions. The mean postoperative CCU stay was reduced by over one day in the OPCAB group. For patients older than 80 years of age, there was a two-fold decrease in neurologic complications (7.1% versus 13.8%) and a four-fold decrease in renal complications (3.6% versus 15.5%) between the off-pump and on-pump groups. The incidence of postoperative bleeding requiring reexploration was highest in this elderly subgroup (8.6%) if CPB was used, but was 0% if done off-pump.
For the reoperation subgroup, the reduction in the incidence of intraoperative transfusion was most marked. The incidence of renal complications and postoperative bleed was less, but the incidence of neurologic complications was more in the off-pump versus the on-pump reoperation patients.
| Comment |
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Of the variables studied in the overall series, OPCAB significantly affected only the incidence of intraoperative transfusion, although an improved OPCAB mortality rate approached statistical significance. Neurologic, renal, coagulopathic, and prolonged ventilator complications were all reduced in the OPCAB group, and although the results were not statistically significant, the trends were consistent.
It is reasonable to suspect that patients at highest risk for undergoing CPB and cardioplegic arrest, including those with advanced age, ventricular dysfunction, stroke, COPD, renal failure, or prior CABG, would be precisely those patients in whom OPCAB would likely have the most beneficial impact. Looking at these various high-risk subgroups, the only variable that was found to yield a statistically significant difference between on-pump and off-pump groups was intraoperative transfusion requirement. This reduced incidence of transfusion requirement in OPCAB is likely related to inflammatory and coagulopathic sequelae intrinsic to CPB, as well as the hemodilution effect of the pump priming fluid.
No patient with COPD who underwent OPCAB required prolonged mechanical ventilation, compared to 9.3% of standard CABG patients, likely related to fluid shifts and damaging inflammatory effects inflicted by CPB on an already compromised lung. Interestingly, all other high risk subgroups who underwent OPCAB had some patients requiring prolonged ventilator support (although still generally less than the on-pump groups). The reason COPD patients undergoing OPCAB had the least incidence of prolonged ventilatory requirements compared to other high-risk subgroups is unclear, but may be related to a greater preoperative awareness and initiation of pulmonary treatment protocols.
Adverse cerebral outcomes after coronary bypass surgery increase dramatically in elderly populations, and were believed to be largely due to CPB and aortic manipulation [13]. Cognitive changes after CABG, however, appear to be a much more multifactorial problem associated with medical as well as surgical variables [14]. These variables include the nonspecific effects that anesthesia and any prolonged surgery with or without CPB have on the cognitive status of elderly patients in general. In our series, 5% of all patients undergoing standard CABG sustained a neurologic complication, but of the patients 80 years of age or older, 13.8% sustained a neurologic complication, approximating the findings of Roach and colleagues [13]. In our OPCAB patients, there was an overall 3.3% incidence of neurologic complications, but of the OPCAB patients 80 years of age or older, there was a 7.1% incidence. Elimination of CPB seemed to reduce the incidence of neurologic complications, particularly in the elderly population, but certainly did not eliminate neurologic complications. Furthermore, in patients who had preoperative strokes or transient ischemic attacks, OPCAB and standard CPB did not substantially differ in our series in the relatively high incidence of postoperative neurologic complications (12% to 14%).
In the preoperative renal insufficiency subgroup, OPCAB decreased the incidence of further renal deterioration. A recent prospective randomized study showed that glomerular filtration (creatinine clearance) and renal tubular function were significantly improved in off-pump compared to on-pump CABG [14]. The authors concluded that OPCAB offered superior renal protection compared to standard CABG.
OPCAB has been shown to reduce myocardial injury and troponin I release compared to standard CABG with cardioplegic arrest [4, 7]. This could presumably translate into improved clinical results, particularly for the most severely compromised ventricles. In our subgroup of patients with profoundly impaired ventricles with ejection fraction less than or equal to 0.25, early postoperative ventricular function was not routinely evaluated by echocardiography or ventriculography. Besides the reduction in transfusion requirements, no obvious differences between the off-pump and on-pump groups were readily apparent. There was a higher incidence of renal complications in the OPCAB group, but this was likely related more to intrinsic patient factors than to merits of standard CPB.
A point worth mentioning is that all our patients, despite their profound ventricular dysfunction, were in New York Heart Association functional classes I and II at the time of surgery. This likely contributed to the similarly low morbidities and mortalities for both on-pump and off-pump groups. More pronounced differences between the groups would have probably been found if the patients had undergone emergency surgery while in heart failure.
Patients of advanced age of 80 years or older are in a high-risk subgroup that would be expected to benefit substantially from eliminating CPB. As mentioned above, neurologic complications were reduced in the OPCAB group. Furthermore, renal complications, postoperative bleeding, and mortality were also all reduced in the OPCAB group. The individual organ systems of patients with advanced age seem to be particularly at risk for the pathophysiologic sequelae of CPB.
Reoperations exhibited a marked difference in the incidence of intraoperative blood transfusions for OPCAB. This is a reasonable prediction considering the dissection necessary to clear adhesions and CPB-mediated activation of inflammatory and coagulopathic cascades on raw surfaces.
In all these high-risk subgroups, there were no operative mortalities for OPCAB, with mortalities for CPB groups ranging from 2.3% to 8.3%. With few exceptions, OPCAB reduced the incidence for every complication studied when compared to on-pump groups, as well as reducing postoperative CCU and hospital stays. While not statistically significant, the trends were nonetheless consistent.
We conclude that eliminating CPB in coronary revascularization reduces the incidence of intraoperative blood transfusion requirements. Our study further supports the provocative possibility that obviating the need for CPB and cardioplegic arrest may improve clinical outcomes, particularly in some high-risk groups such as the elderly and those with specific organ dysfunction. Anatomic factors, however, including cardiomegaly and small, intramyocardial, or heavily calcified vessels requiring endarterectomy may preclude OPCAB in some instances. Refinements in routine on-pump CABG have reduced morbidity and mortality rates to the point that subtle differences in clinical outcomes would only be expected to manifest statistical significance in a large series. Nonetheless, the physiologic rationale for avoiding or limiting CPB and cardioplegic arrest remains sound, particularly for at-risk patient populations.
| Footnotes |
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| References |
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